Method for Detecting Pixel Outliers

1. In a digital image including a plurality of pixels, a method for identifying singleton outlier pixels in a selected color space comprising: for each 3×3 patch of pixels in the image, calculating the diameter of the 3×3 patch of pixels; for each pixel in the patch, computing the distance to its nearest neighbor pixel within the patch, as measured in the selected color space; comparing the computed distance from each pixel in the patch to its nearest neighbor with a threshold that is a preselected fraction of the diameter; and identifying a center pixel in the patch as an outlier pixel if its calculated distance to its nearest neighbor is the largest distance to a nearest neighbor and exceeds the threshold.

2. The method of claim 1 wherein the selected color space is sRGB space.

3. The method of claim 1 wherein the distance is the squared Euclidean distance.

4. The method of claim 1 , wherein the preselected fraction of the diameter is about 0.1.

5. In a digital image including a plurality of pixels, a method for identifying pairs of adjacent outlier pixels in a selected color space comprising: for each 3×3 patch of pixels in the image, calculating the minimum diameter of the 3×3 patch of pixels; for each pixel in the 3×3 patch, computing the distance to its nearest neighbor pixel within the 3×3 patch, as measured in the selected color space; comparing the computed distance from each pixel in the 3×3 patch to its nearest neighbor with a threshold that is a preselected fraction of the minimum diameter; if the calculated distance to the nearest neighbor of a center pixel in the 3×3 patch is not both the largest distance to a nearest neighbor in the 3×3 patch and does not exceed the threshold, making a set of comparisons of the computed distance from non-center pixels in the 3×3 patch to its nearest neighbor with a threshold that is a preselected fraction of the diameter, each comparison in the set made by ignoring a different one of the non-center pixels in the 3×3 patch; if in only one of the comparisons in the set, the calculated distance from the center pixel to its nearest neighbor is the largest distance to a nearest neighbor and exceeds the threshold: define a new 3×3 patch of pixels having the ignored pixel in the identified comparison as the new center pixel; for each pixel in the new 3×3 patch, computing the distance to its nearest neighbor pixel within the new 3×3 patch, as measured in the selected color space; comparing the computed distance from each pixel in the new 3×3 patch to its nearest neighbor with a threshold that is a preselected fraction of the minimum diameter; if the calculated distance from the new center pixel to its nearest neighbor in the new 3×3 patch of pixels is the largest distance to a nearest neighbor and exceeds the threshold, identify the center pixel and the new center pixel as a pair of adjacent outlier pixels.

6. The method of claim 5 wherein the selected color space is sRGB space.

7. The method of claim 5 wherein the distance is the squared Euclidean distance.

8. The method of claim 5 , wherein the preselected fraction of the minimum diameter is about 0.1.